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Bathroom venting to Attic

Our new old home has the bathroom venting to the attic. We are looking correct this somehow.

My father in-law has asked that we buy non-insulated tubing and cut a hole directly above in the roof.

My uncle has suggested that we purchase insulated tubing to prevent condensation. Then route to the exhaust vent, he is expressing concern that cutting additional holes in the roof could through time expose additional problems aka leakage.

What is the most common practice, and what risks are we incurring by adding additional cutouts in the roof?

Re: Bathroom venting to Attic

Properly done, venting to the roof is not a problem. It is very common and probably the preferred method. (You do not want to vent to the soffits but you might be able to vent out a side gable in the attic just as long as the moist air isn’t going to get pulled back into the attic – check with your local building inspector.) My house (built in 1990) has both upstairs baths vented to the roof. You will have to install a vent cap on the roof where the vent pipe exits. (If you are not comfortable working on your roof then you should hire this out.) The vent “pipe” is flexible and insulated. I’d definitely use insulated. Also, make sure you properly flash the vent cap or you could have leaks.

I reroofed my house in 2003 and found a problem with how the original venting was done. The vent hose has a square metal plate which attaches to the back side of the roof sheathing. The moist air was able to get into the roof sheathing. You can see in the attached picture that the sheathing is blackened and rotten. I replaced the rotten pieces of OSB. Then I put a section of ice and water shield (a very sticky waterproof membrane) on the back side of the roof sheathing between it and the metal plate on the vent pipe. After I had attached the metal plate to the underside of the roof sheathing I cut strips of the ice and water shield and fit them down the “throat” of the vent pipe from the top. This totally prevents any moist air from coming in contact with the roof sheathing or escaping into the attic. (I also had ice and water shield on the top of the roof sheathing.)

Re: Bathroom venting to Attic

Originally Posted by butrflynlambie

My father in-law has asked that we buy non-insulated tubing and cut a hole directly above in the roof.

I certainly don't agree... you should use insulated ducting.

My uncle has suggested that we purchase insulated tubing to prevent condensation. Then route to the exhaust vent, he is expressing concern that cutting additional holes in the roof could through time expose additional problems aka leakage.

What is the most common practice, and what risks are we incurring by adding additional cutouts in the roof?

I agree with your uncle.
As for common practice... this can vary as to region but it seems that roof venting is common overall.

The idea of a leak proof roof is to have a monolythic covering and each time it becomes interuppted with an opening for vents and the like is an oppourtunity for a leak. If done properly this can be done with minimul problems though any imperfections will allow water pentration.